Optimization of Screw Press Dewatering Using Statistical Analysis, 1995 Environmental Conference Proceedings

John W. Sparapany

Nalco Chemical Company

Jenny Weibel

Simpson Tacoma Kraft Company

Many factors can influence the efficiency of dewatering paper mill biosolids/lost fiber using screw presses. Biosolids are the most difficult solids to dewater and, with improvements in fiber recovery processes, the ratio of lost fiber to biosolids being dewatered is generally decreasing. To maintain or improve screw press dewatering efficiency, the polymer treatment program can be evaluated and changed if necessary. However, altering the screw press dewatering parameters can also significantly improve dewatering efficiency. An experimental design was run on two screw press applications to determine the impact of operating variables on cake solids, cake throughput, polymer demand and filtrate clarity. Analysis of the data showed that the screw press could be optimized to handle the increased biosolids loading while maintaining cake solids. Output of cake and polymer dosage can be maintained under certain operational conditions. The analysis demonstrated that the variables are dependent on each other. Altering one variable can result in required changes in other operational parameters to achieve an improvement in dewatering.